The present invention relates to a satellite system being comprised of at least two interconnected bodies or modules respectively constituting power supply and service module, and payload modules.
Satellites or satellites systems orbiting the earth are usually oriented in relation to the sun. Their position or attitude is, for example, determined on the basis of spin moments or, if such an effect is undesirable, orientation is provided through follower control with respect to certain reference aspects. Known satellite systems may, for example, be comprised of two bodies which are rotatable in relation to each other, and one rotates for purposes of attitude stabilization with respect to the other one; the latter remaining stationary as far as that rotation is concerned accordingly. The latter body moreover will constitute the basic component. During operation it is necessary to maintain the satellite in a relatively stable and uniform orientation vis-a-vis space. This orientation is usually maintained under utilization of the spin effect, i.e., the satellite or a portion thereof (momentum wheel) rotates continuously about a fixed axis. Utilization of this effect is further enhanced if one provides a non-rotating payload platform or the like, whose orientation is maintained vis-a-vis the earth, and serving primarily as payload device.
In accordance with another aspect, it is known to stabilize a satellite vis-a-vis three axes, each of them are oriented vis-a-vis a reference point. Appropriate sensors provide follow-up control, and a suitable torque control devices maintain dynamically and actively the desired attitude and orientation. This kind of approach is usually used if the spinning proves to have too many undesirable side effects.
Turning back to a basic satellite system composed of two modules, one has to consider that in fact two different planes of orientation are needed. The service module is oriented basically vis-a-vis the sun as a primary source of energy. On the other hand, the payload is oriented usually towards the earth for reasons of communication, observational features, etc. (see e.g. U.S. Pat. No. 4,374,579). One can see, however, that the service module is the immediate source of energy for the equipment in the satellite and is primary as far as various motions is concerned. For example, the solar generator of the service module has to track faithfully the sun while the orientation of the payload towards the earth should remain independent from this solar tracking. This then has led to the point that permanent connections are provided between the payload module and the service module, and the arrangement of the two must follow particular sequence.